Microfiche reader

ABSTRACT

A microfiche reader according to the present invention includes a housing consisting of a hood portion and a base portion, a screen located within the hood portion and visible through the front end of the hood, a combined microfiche carriage and index holder, a lens assembly and a projection system. The combined microfiche carriage and index holder serves to accurately locate the microfiche with respect to the index grid. By reason of the fact that there is no relative movement between the index grid and the microfiche in use, it is always possible to accurately locate the microfiche with respect to the projection system by reference to the index grid. The index grid is illuminated by an index illuminating lens carried by the housing. The illuminating lens is located in a fixed relationship with respect to the projection path which again contributes to the facility with which the microfiche may be accurately located in the projection path. The lens assembly includes a support plate mounted above the microfiche carriage and a slide member mounted in the support plate and a pair of lens members mounted in the slide members so that either one may be located in the projection path as required. The projection system includes a demountable modular unit which may be easily mounted in and removed from the housing. A prefocussed lamp is mounted on the modular unit and the position of the prefocussed lamp with respect to the modular unit may be adjusted so as to vary the length of the illuminating path between the prefocussed lamp and the condenser means whereby the optical system may be adjusted to accommodate objective lenses having different characteristics. The projection system consists of a prefocussed lamp which projects a beam of light onto a cold mirror which reflects the beam of light through an optical condenser which in turn directs the beam of light through the micromirror is mounted in the housing and reflects the beam of light emitted from the objective lens to a viewing screen mounted in the housing. The viewing screen consists of a unitary body of molded plastics material having an image receiving surface formed with a concave spherical curvature. The image receiving surface may be plated with a suitable coating to form an image reflecting coating thereon.

This is a division of application Ser. No. 777,772, filed Mar. 15, 1977,now U.S. Pat. No. 4,140,376.

This invention relates to improvements in a microfiche reader. Inparticular, this invention relates to improvements in a front projectiontype of microfiche reader.

PRIOR ART

In the microfiche readers which are presently available, a microfiche islocated in a movable holder for movement with respect to theilluminating path of the projection system and a corresponding gridpattern is located in a stationary position with respect to themicrofiche housing. The microfiche holder has an indexing fingerprojecting outwardly therefrom to overlie the indexing grid. Theindexing finger may be located at any position with respect to theindexing grid to locate the corresponding portion of the microfiche inthe projection path. Because the microfiche holder and, therefore, themicrofiche is movable relative to the indexing grid, the microfiche maybe slightly misaligned with respect to the grid making the location of aspecific area of the microfiche difficult at times. In addition, theclearances between the relatively moving components of the microficheholder and indexing grid are such that difficulties can be experiencedin obtaining correct alignment of the microfiche.

I have overcome the above difficulties by reason of the fact that theindexing grid and microfiche are mounted in a unitary microfichecarriage and index holder so that no relative movement occurs betweenthe indexing grid and the microfiche when the apparatus is in use.

Considerable difficulty has also been experienced in attempting toprovide an undercarriage support system for the microfiche carriagewhich will adequately support the carriage for movement with respect tothe projection path of the reader. This difficulty has been overcome byproviding an undercarriage which has V-shaped support rails and V-shapedwheels cooperating with one another and rails on the support platform ofthe microfiche reader to provide a minimum backlash in the system inresponse to movement of the microfiche carriage.

In a microfiche reader it is important to ensure that the microfiche maybe located in and removed from the microfiche carriage as easily aspossible. I have achieved this desirable result by providing an upperglass flat which is automatically raised as the microfiche carriage ismoved to a predetermined position forwardly of the platform of thereader to provide access to the microfiche for removal.

The servicing of the projection system of a microfiche reader isgenerally limited to a requirement that the illuminating light may bereadily replaced. This is achieved in accordance with one aspect of thepresent invention by reason of the fact that the lamp is mounted in amodular unit which may be removed from the reader housing.

In many instances it is desirable to be able to change the objectivelens of a microfiche reader so that the reader may be used for a varietyof purposes. When the objective lens is changed in the known readers,considerable adjustment of the optical system is required. Thisdifficulty is overcome by one aspect of the microfiche reader of thepresent invention which provides a prefocussed lamp which is mounted tobe adjustably movable towards and away from the condenser lens of theprojection system whereby the projection system may be adjusted toaccommodate objective lenses having different characteristics by themovement of the position of the prefocussed lamp with respect to thecondenser lens. Preferably the prefocussed lamp is mounted to beadjustably movable with respect to the modular unit which is removablefrom the main housing of the reader.

To adjust the magnification of the projected image in known microfichereaders., the objective lens is removed and replaced by another lens.This adjustment requires a knowledge of the structure of the microfichereader assembly and can create difficulties for operators not familiarwith the structure. This difficulty has been overcome according to oneaspect of the microfiche reader described herein by mounting a pair ofobjective lenses in a slide member which is slidably mounted in asupport plate above the microfiche carriage, the lenses being releasablysecured in the illuminating path of the projector as required in use.

The majority of microfiche readers presently in use have a projectionsystem which requires a power-driven fan in order to provide adequatecooling. Because of the very substantial amount of heat generated by theconventional optical system, it has been necessary to make the housingsrelatively large and to provide a powerful fan-driven cooling system.The fan-driven cooling system is noisy and creates a further source ofservice difficulties. These difficulties are overcome by one aspect ofthe apparatus described herein which provides an optical system andventing system and housing construction which permits the microfichereader to operate without the use of a forced-air cooling system.

Considerable difficulty has also been experienced in providing a screenfor a microfiche reader which has adequate reflective characteristics tofunction effectively as a screen in a front projection system. Thescreen of the microfiche reader according to one aspect of the presentinvention overcomes this difficulty and is formed from a unitary body ofmolded plastics material which has an image receiving surface formedwith a concave spherical curvature and which is coated with a layer ofan image reflecting material.

SUMMARY OF INVENTION

According to one aspect of the present invention, there is provided in amicrofiche reader of the type having a housing, an image projectionsystem including projector means and a screen for receiving a projectedimage and an illuminating path extending from the projector means to thescreen, the improvement of a combination microfiche carriage and indexholder which comprises a frame, a first window opening through saidframe, means for locating a microfiche in a predetermined position withrespect to said first window for the projection of light therethrough, asecond window opening through said frame, a transparent index gridmounted in said second window in a predetermined position with respectto said second window for the projection of light therethrough, indexilluminating means underlying said second window and located in a fixedrelationship with respect to a portion of the illuminating path whichprojects through said first window opening, said frame being mounted forplanar movement with respect to said housing to locate any required areaof the grid in the beam of light emanating from the index illuminatingmeans and thereby to locate the corresponding areas of the microfiche inthe illuminating path of the projector for projection onto the screen.

According to a further aspect of the present invention, there isprovided in a microfiche reader of the type having a housing, an imageprojection system including projector means and a screen for receiving aprojected image and an illuminating path extending from the projectormeans to the screen, a microfiche carriage having an upper glass flatarranged to be disposed above a microfiche in the carriage, theimprovement of a lens assembly which comprises a support plate mountedabove said microfiche carriage, passage means opening through saidsupport plate in alignment with the illuminating path of said projector,a slide member mounted in said support plate for movement relativethereto, a pair of lens passages opening through said slide member, alens holder mounted in each of said lens passages, a lens memberreleasably mounted in each of said lens holders, said carriage meansbeing slidable relative to said support plate to locate one or other ofsaid lens members in said illuminating path of said projector, andreleasable lock means for releasably locking either of said lens membersin said illuminating path in use.

According to a further aspect of the present invention, there isprovided a microfiche reader of the type having a housing, a viewingscreen located within said housing and a projection system forprojecting an illuminating beam of light along an illuminating path,said illuminating beam being directed through a condenser lens, amicrofiche and an objective lens arranged in series and onto saidscreen, the improvement wherein said projection system includes ademountable modular unit which comprises a frame removably mounted in anoperative position in said housing, mirror means mounted in said framein a fixed position with respect to said frame, said mirror means beinglocated in said illuminating path when said frame is in said operativeposition, a prefocussed lamp mounted in said frame for movement towardsand away from said mirror means to vary the length of the illuminatingpath between the prefocussed lamp and the condenser means whereby theoptical system may be adjusted to accommodate objective lenses havingdifferent characteristics.

According to a further aspect of the present invention, there isprovided a microfiche reader of the front projection type having ahousing, a microfiche carrier mounted in said housing and a projectionsystem for projecting an illuminated image from a microfiche, theimprovement wherein said projection system comprises a prefocussed lampmounted in said housing providing a source of a beam of light, a coldmirror mounted in said housing in the path of the beam of light emittedfrom said prefocussed lamp for reflecting said beam, an opticalcondenser mounted in said housing in the path of the beam of lightreflected by said cold mirror, said optical condenser directing the beamof light through the microfiche carrier, an objective lens mounted insaid housing for receiving the beam of light transmitted through saidmicrofiche carrier, a first surface mirror mounted in said housing inthe path of the beam of light emitted from said objective lens, aviewing screen mounted in said housing for receiving the illuminatedbeam of light reflected from said first surface mirror, said prefocussedlamp being adjustable towards and away from said optical condenserwhereby the projection system may be adjusted to accommodate objectivelenses having different characteristics.

According to a further aspect of the present invention, there isprovided a microfiche viewer having a housing, a screen mounted in saidhousing and a front projection system for projecting images from amicrofiche onto a screen, the improvement wherein said screen comprisesa unitary body of molded plastics material having an image receivingsurface formed with a concave spherical curvature, said image receivingsurface being coated with a layer of image reflecting material.

According to a further aspect of the present invention, there isprovided a microfiche viewer having a housing, wherein the screen has anupper edge and a lower edge, and a pair of side edges, said side edgesconverging with respect to one another whereby the screen has an imagereceiving surface which is narrower at said upper edge than it is atsaid lower edge to conform to the configuration of the projected image.

The invention will be more clearly understood after reference to thefollowing detailed specification read in conjunction with the drawingswherein,

FIG. 1 is a pictorial front view of a microfiche reader according to anembodiment of the present invention;

FIG. 2 is a top view of the platform of the microfiche reader and anexploded view of the microfiche carriage of FIG. 1;

FIG. 2a is an exploded top view of the platform of the microfichereader;

FIG. 3 is an exploded view of the hood portion of the microfiche readerof FIG. 1;

FIG. 4 is a sectioned pictorial view of the lens support plate;

FIG. 5 is a pictorial view of the lens holder assembly;

FIG. 6 is a pictorial back view of the screen;

FIG. 7 is a diagrammatic illustration of the projection system andindexing system of the microfiche reader;

FIG. 8 is a pictorial side view of the microfiche carriage located onthe support platform of the microfiche reader;

FIG. 9 is a sectional view through a support rail and the undercarriageillustrating the rail and wheel configuration.

A microfiche reader according to an embodiment of the present inventionis illustrated in FIG. 1 of the drawings. In FIG. 1 of the drawings, thereference numeral 10 refers generally to the microfiche reader housingwhich consists of a hood portion 12 and a base portion 14. A screen 16is located within the hood 12 and is visible through the front end ofthe hood. A combined microfiche carriage and index holder 18 issupported on the base portion 14 and is mounted for movement withrespect to the base portion. A lens assembly 20 is mounted in the hood12 and disposed above the carriage 18.

MICROFICHE CARRIAGE

The structure of the combined microfiche carriage and index holder 18and its support structure is illustrated in FIGS. 2, 8 and 9 of thedrawings. The combined microfiche carriage and index holder 18 consistsof a frame 22 which has a first window 24 opening therethrough and asecond window 26 opening therethrough. The lower glass flat 28 (FIG. 8)is located in the first window 24 and an upper glass flat holder 30 ispivotally mounted by means of lugs 32 in recesses 34. The lugs 32 formhinges about which the upper glass flat 30 may pivot so as to be raisedout of engagement with the lower glass flat 28. An actuator extension 36extends rearwardly and upwardly from the back edge of the upper glassflat holder. The actuator extension 36 engages the lug 38 located on theunderside of the lens support plate 40 (FIG. 3) so that when thecarriage 18 is moved outwardly towards the operator, the actuatorextension will at a predetermined location cause the upper glass flat topivot upwardly to facilitate the location of a microfiche 44 between thelower glass flat 28 and the upper glass flat 30. An index grid 46 islocated in the second window 26. Two sets of ribs 48 extend across theunderside of the carriage 18 in a spaced parallel relationship.

As shown in FIG. 9 of the drawings, a V-shaped wheel 50 is mounted forrotation on a shaft 52 which is supported by the ribs 48. A plurality ofwheels 50 are located in this manner in a channel 54 formed between theribs 48 at spaced intervals along the length of the ribs. A rectangularshaped undercarriage 56 is formed with a pair of support rails 58extending transversely thereof and a pair of U-shaped channel members 60extending longitudinally thereof. As shown in FIG. 9 of the drawings,each of the rail members 58 has a V-shaped rail portion 62 which isproportioned to support the V-shaped wheels 50. A plurality ofadditional wheel members 50 are located in the U-shaped channel members60 at spaced intervals along the length thereof. Channels 64 are formedin the surface of the platform 66 of the base member 14. Support rails68 of the same contour as the rails 62 extend longitudinally of thechannels 64. A narrow lip portion 70 projects outwardly from an outerside edge of each channel 64. In use, the lip 70 overlies the ledge 72which projects outwardly from the side of the U-shaped channel members60 and serves to retain the undercarriage 56 in engagement with the railmember 58.

To mount the undercarriage 56 on the platform 64, it is located towardsthe front end of the platform and lowered to a position in which thewheel members 50 carried by the undercarriage rest on the support rails64. The carriage 22 is mounted on the undercarriage 56 by locating thewheel members 50 on the guide rails 62. Longitudinal movement of thecarriage 18 with respect to the reader is achieved by the movement ofthe undercarriage 56 along the support rails 68 and transverse movementis achieved by transverse movement of the carriage 26 with respect tothe undercarriage 58 by the movement of the support wheels 50 along theguide rails 62.

As shown in FIGS. 2 and 2a of the drawings, an index illuminatingpassage 74 opens through the wall of the platform 66 centrally of thewidth thereof. An index illuminating lens 76 is located in the passage74 and serves to concentrate the light emitted through the passage 74.As will be described hereinafter, light emitted from the lens 76 passesthrough the indexing grid 46 and serves to provide a method of locatinga required location on the microfiche by reference to the illuminatedgrid.

THE BASE MEMBER

The base member 14 has a bottom wall 80 (FIG. 2a) extending from theback face thereof towards the front face. An angularly inclined bottomwall 82 extends upwardly and forwardly from the bottom wall 80 to afront wall 86 which extends vertically upwardly to the platform 66. Aninner wall 88 extends upwardly from the platform and a top wall 90extends rearwardly from the inner wall 88 to the back wall 93. A pair ofguide rails 92 are located on the inner face of the bottom wall 80. Aplurality of vent openings 94 are located in the bottom wall 80 and inthe inclined bottom wall 82. An operating switch 95 is mounted in thefront wall 86. Vent passages 96 are located in the platform 66. Acondenser passage 98 opens through the platform 66. Air circulationpassages 100 and 101 open through the top wall 90 and back wall 93respectively. A lamp mounting passage 102 opens through the back wall 93of the base.

A removable drawer 104 is proportioned to extend through the passage 102in the back wall so as to be located within the base 14 with the backplate 106 thereof closing the passage 102. The drawer 104 has a bottomwall 108, the opposite side edges of which are adapted to fit within thetrack formed by the guide rails 92. An electrical plug member 110 islocated at the inner end of the drawer 104 and is adapted to fit withina socket 112 located in the base 14 when the drawer is located in anopposite position within the base. A prefocussed lamp 114 is adjustablymounted on the bottom wall 108 by means of a mounting bolt 115 which isthreaded and which extends through a passage 116 in the bottom wall 108and is clamped by means of a nut 118 and a spring washer 120.

The lamp 114 and its associated housing may be moved longitudinally ofthe bottom wall 108 to any required position. The lamp 114 iselectrically connected to the plug member 110 by wires 122 such thatwhen the drawer 104 is located in an operative position within the base,electrical power is supplied to the prefocussed lamp 14.

The electrical power is supplied to the microfiche reader as a whole bymeans of cable 126. The electrical power is supplied to the transformer128 which is located in the housing and the transformer 128 iselectrically connected to ON/OFF switch 95 by lines 130.

HOOD STRUCTURE

The structure of the hood 12 is illustrated in FIGS. 1 and 3 of thedrawings. As shown in FIG. 3 of the drawings, the hood 12 has a pair ofside walls 132, a top wall 134, an upper back wall 136, a lower backwall 138 and a bottom wall 140. A passage 142 opens between the lowerback wall 138 and the bottom wall 140. A screen support shoulder isformed about the inner edge of the passage 142 and consists of sideshoulder portions 144, top shoulder portion 146 and bottom shoulderportion 148. A pair of support lugs 150 (only one shown) are located atthe lower edge of each side wall 132 and serve to support the lenssupport plate 40 as will be described hereinafter. The bottom wall 140is formed with a plurality of air circulating vent passages 152. Thehood 12 is mounted on the base 14 with the bottom wall 140 supported bythe top wall 90 of the base. Mounting screws 154 secure the hood withrespect to the base. A window mounting lip 156 is located at the frontedge of the hood to secure a window 158 therein. The screen 16 hasmounting passages 160 (FIG. 6) in the back face thereof which arethreadably engaged by mounting screws 162 (FIG. 3) which extend throughpassages 164 formed in the upper screen mounting shoulder 146 to securethe screen with respect to the housing in the position shown in chainlines in FIG. 3. A highly reflective mirror 165 is mounted on the innerface of the top wall 134 of the hood to reflect images projected thereononto the screen 16.

SCREEN

The screen 16 is made from a unitary body of molded plastics materialsuch as A.B.S. The image receiving surface 166 of the screen has aconcave spherical curvature. The side edges 168 of the screen convergewith respect to one another in a direction towards the upper edge of thescreen. It has been found that the configuration of the image receivingsurface achieved by providing a concave curvature both longitudinallyand transversely of the screen and by reducing the width of the screentowards the upper end is most suitable for receiving images projected bythe projection system described hereinafter. The unitary body of thescreen 16 includes side walls 170, top wall 172, bottom wall 174 and apair of diagonally extending reinforcing webs 176. The inner edge of theside walls is shaped to follow the configuration of the hood in which itis mounted. The image receiving surface 166 of the screen is plated witha layer of silver or the like to form an image reflecting coatingthereon.

LENS ASSEMBLY

The lens assembly 20 is illustrated in FIGS. 3, 4 and 5 of the drawings.The lens assembly 20 consists of a support plate 40 which is mounted onsupport lugs 150 of the hood 14 by means of mounting screws 180. Thesupport plate 40 has a passage 182 opening therethrough. As shown inFIGS. 3 and 4 of the drawings, a support rail 184 is located below theside edges of the passage 182 in a spaced relationship with respect tothe support plate 40. A slide member 186 has a central portion 188 whichis substantially shorter in length than the passage 182. The slidemember 186 also has a pair of end portions 190 which are thinner thanthe central portion 188. The slide member 186 is mounted in the supportplate 40 and is supported therein by support rails 184. The centralportion 188 of the slide member projects into the passage 182 and theend portions 190 underlie the support plate 40 at opposite ends of thepassage 182. By reason of the fact that the central portion 188 isshorter than the passage 182, the slide member 186 may be moved back andforth in the passage 182. The front support rail 184 has a notch 192opening therethrough which serves to operably locate the requiredobjective lens in the projection path as will be described hereinafter.The slide member 186 has a pair of tubular sleeve projections 194projecting downwardly therefrom. The sleeve projections 194 havepassages 196 opening therethrough. A longitudinal slot 198 also opensthrough each sleeve projection at the front end thereof, a portion ofthe slot 198 also opening through the central portion 188 of the slideinto the passage 196. A pair of lens holders 200 are adapted to fitwithin the passages 196. Each of the lens holders 200 has a keyprojection 202 extending longitudinally thereof. The key 202 has a lipportion 204 at the upper end thereof which projects outwardly from themain body. The main body of the key 202 is adapted to fit in a closefitting relationship within the slot 198 so that the lens holder member200 may drop downwardly through the passage 196 when the key portion 202is aligned with the notch 192 in the support rails 184 of the supportplate 40. When the key 202 is cut of alignment with the notch 192, thelip portion 204 rides along the support rail 184 and holds the lensholder in a raised position. Objective lenses 206 and 207 are threadablymounted in the lens holders 200. The objective lenses 206 and 207 have ahousing 208 which has a greater diameter than the diameter of thepassage 196 in the slide member 186 so that the housings 208 limit theextent to which the lenses may drop relative to the slide member 186.

PROJECTION SYSTEM

The image projection system is illustrated in FIG. 7 of the drawings. Asshown in FIG. 7 of the drawings, light emanating from the prefocussedlamp 114 travels along the path 210 and is reflected by a first coldmirror 212 which, as shown in FIG. 2 of the drawings, is mounted in thedemountable drawer 104. The light is reflected by the mirror 212 alongthe path 214 to a condenser lens 216. The condenser lens 216 is mountedin the passage 98 formed in the platform 66 of the base 14. The lightbeam passes through the condenser lens 216 and is directed along thepath 218 through a portion of the microfiche 44. The image carried bythe microfiche 44 is projected through the objective lens 206 along thepath 220 onto the first surface mirror 165. The image is reflected fromthe mirror 165 along the path 222 onto the image receiving surface 166of the screen 16. The lamp 114 illuminates the interior of the base 14and the light from within the base is emitted through the indexilluminating lens 76 along the path 224 which projects through the indexgrid 46. By reason of the fact that the index grid 46 and microfiche 44are mounted in the combined microfiche carriage and index holder 18 in afixed relationship with respect to one another and the fact that theindex illuminating beam of light travels along a path 224 which islocated in a fixed relationship with respect to the path 218 of themicrofiche illuminating light beam, it is possible to locate anyrequired portion of the microfiche in the projection path by locatingthe corresponding portion of the index grid in the index illuminatingpath. The slide member 190 is movable so as to permit either one of theobjective lenses 208 to be located in the path 218. In use, theobjective lenses 208 may have different magnifications so that themagnification of the microfiche reader may be adjusted by the simple actof moving the slide 190 to and fro to align the required objective lenswith the image projecting path 218. Similarly, the carriage 18 ismovable relative to the condenser lens 216 in the direction of theX-axis and in the direction of the Y-axis shown in FIG. 7. This mobilityof the carriage 18 permits any portion of the microfiche 44 and indexgrid 46 to be located in the paths 218 and 224 respectively so that anyportion of the microfiche 46 may be projected onto the image receivingsurface 166 of the screen 16.

OPERATION

Prior to operation of the microfiche reader, the required objectivelenses are selected. The optical characteristics of the objective lensesmay be such that it is necessary to adjust the position of theprefocussed lamp 114 with respect to the condense lens 216 in order tofocus the beam emitted from the condenser lens 216 on the objective lens207. As previously indicated, the prefocussed lamp 114 is adjustablewith respect to the drawer 104. The position of the prefocussed lamp 114is, therefore, adjusted by releasing the clamping nut 118 and moving thelamp 114 longitudinally of the bottom wall 108 of the drawer.

In order to locate the microfiche 44 in the microfiche holder 18, themicrofiche holder 18 is moved in the direction of the X-axis (FIG. 7)until the upper glass flat 30 is elevated by engagement of the actuatorlip 36 with the tongue 38 which projects downwardly from the supportplate 40. The microfiche 44 is then located between the upper and lowerglass flats 28 and 30 and the carriage 18 is moved inwardly, as a resultof which the upper glass flat 30 is lowered into a face-to-facerelationship with the microfiche 44.

As previously indicated, one of the objective lens members 208 isaligned with the path 218. The lens holder 200 of the aligned objectivelens rests on the upper glass flat 32 while the lens holder of thenon-aligned objective lens is held in a spaced relationship above theupper glass flat 32. When the lens holder 200 is aligned with theprojection path, the key 202 and lug 204 are free to slide in the notch192 in the support rails 184. By reason of the fact that the lower endof the aligned lens holder rests on the upper glass flat, the distancebetween the objective lens and the microfiche 44 is a constant andconsequently the objective lens can be accurately located with respectto the microfiche and with respect to the image receiving surface 166 ofthe screen 16.

When the microfiche is operably located in the microfiche holder 18, asdescribed above, the microfiche holder 18 may be moved to align anyrequired portion of the index grid with respect to the indexilluminating lens 74. The beam of light emitted through the illuminatinglens 74 will illuminate the section of the grid corresponding to theportion of the microfiche which projected onto the screen. In thismanner, any required portion of the microfiche may be projected onto thescreen by reference to the illuminated section of the index grid.

SUMMARY

From the foregoing it will be apparent that the microfiche readerdescribed above provides a number of improvements over the knownstructures. In one such improvement, the microfiche reader provides acombined microfiche carriage and index holder 18. By reason of the factthat both the microfiche 44 and the index grid 46 are mounted in a fixedrelationship with respect to one another, it is easier to accuratelylocate the required section of the microfiche with respect to theilluminating path. In addition, the undercarriage support structure forthe combined microfiche carrier and index holder is designed to providefree movement of the carriage 18 with respect to the projection path.The V-shaped profile of the guide rails and support wheels is such thatthere will be a minimum backlash in the guide track system. It will alsobe noted that by reason of the fact that the microfiche is retained in astationary relationship with respect to the index grid, any backlash inthe undercarriage support system does not contribute to any misalignmentof the microfiche with respect to the grid as would be the case in astructure where the microfiche is moved relative to the grid. The factthat the upper glass flat is elevated automatically when the carriage 18is moved to a predetermined forward position greatly facilitates theremoval and placement of the microfiche between the upper and lowerglass flats.

A further improvement is provided in the structure of the lens assemblyin that the assembly provides two lens members, either one of which maybe moved into the projection path as required. Furthermore, the lensassembly is designed to permit the objective lens holder to rest on theupper surface of the upper glass flat thereby positively locating theobjective lens in a set position with respect to the microfiche.

A still further improvement provided by the microfiche reader of thepreferred embodiment is in the structure of the projection system whichincludes a demountable modular unit 104 which supports a prefocussedlamp for movement thereon so that the lamp may be moved towards and awayfrom the condenser lens whereby the optical system may be adjusted toaccommodate objective lenses having different characteristics. Thisprovides for a very simple adjustment of the optical system which is notavailable in existing microfiche reader devices.

A still further improvement provided by further features of themicrofiche reader is in the projection system which includes aprefocussed lamp, a first cold mirror, an optical condenser, anobjective lens, first surface mirror, and a viewing screen, all of whichare mounted in series along the projection path. The viewing screen isformed from a unitary body of molded plastics material and has an imagereceiving surface formed with a concave spherical curvature. The concavespherical curvature of the image receiving surface provides for theminimum distortion of the projected image.

Yet another advantage of the structure of the microfiche reader of thepreferred embodiment is in the fact that it is not necessary to providea forced air cooling system in order to cool the projection system. Theprefocussed lamp is preferably a ninety watt lamp. The base member isformed with a plurality of ventilating passages 94. The base member 14is supported on feet 81 so that it is spaced above its support surfacein use so that air may be admitted through all of the ventilatingpassages 94. The air passes upwardly through the base and a portion ofthe cooling air may be discharged from the base through ventilatingpassages 36 in the upper wall of the platform 66. The remaining portionof the cooled air, which is the major portion of the air, is dischargedfrom the base through the passages 100 in the upper wall 90 to passthrough the passages 152 in the bottom wall 140 of the hood and to bedirected rearwardly from the hood through the passage 142 in the backwall of the hood and thus to atmosphere. It has been found that this aircirculating system provides adequate cooling for a ninety watt ratedprefocussed lamp 114. Furthermore, it has been found that this coolingsystem sufficiently cools the entire housing of the microfiche viewer toan extent that the viewer may be made entirely from an injection moldedplastics material such as Merlon SF600 structured foam plastic. Byreason of the fact that all of the various components of the viewerhousing and carriage may be made from injection molded plastic material,the overall cost of production of the microfiche viewer can be minimizedin a mass production process.

These and other advantages of the microfiche viewer of the presentinvention will be apparent to those skilled in the art.

What I claim as my invention is:
 1. In a microfiche reader of the typehaving a housing, an image projection system in said housing andincluding projector means and a screen for receiving a projected imageand an illuminating path extending from the projector means to thescreen, the improvement of:(a) a combined microfiche carriage and indexholder comprising:(i) a frame; (ii) a first window opening through saidframe; (iii) means for locating a microfiche in a predetermined positionwith respect to said first window for the projection of lighttherethrough; (iv) a second window opening through said frame; (v) atransparent index grid mounted in said second window in a predeterminedposition with respect to said second window for the projection of lighttherethrough; (b) index illuminating means supported by the housing andunderlying said second window and located in a fixed relationship withrespect to a portion of the illuminating path which projects from thehousing through said first window opening; (c) first and second guiderail means carried by said housing and said frame and supporting saidframe for planar movement with respect to said housing to locate anyrequired area of the grid in the beam of light emanating from the indexilluminating means and thereby to locate the corresponding areas of themicrofiche in the illuminating path of the projector for projection ontothe screen, (d) said housing including a base portion having a generallyhorizontally extending support surface, said platform having a front endand a back end, said index illuminating means being located adjacentsaid front end of said platform and said illuminating path extendingthrough said platform at a location spaced rearwardly from said indexilluminating means with respect to said front end whereby said secondwindow opening of said microfiche carriage is located forwardly of saidfirst window with respect to the front end of said platform to bereadily visible, (e) said first guide rail means being located on saidplatform and extending longitudinally from said front end of saidplatform, an undercarriage having first wheel means mounted thereon andengaging said first guide rail means for movement therealong, saidsecond guide rail means being located on said undercarriage andextending normal to said first guide rail means, second wheel means onsaid frame engaging said second guide rail means for movementtherealong, said first and second guide rail means having a V-shapedsupport surface and said first and second wheel means having a V-shapedsurface adapted to outwardly overlie said V-shaped support surface ofsaid first and second guide rail means, said first and second wheelmeans being mounted to rotate about horizontally oriented axes wherebyboth faces of the V-shaped support surfaces support the weight of thecarriage in use, said first guide rail means being recessed below theplatform and the platform being provided with slot means through whichthe first wheel means of the undercarriage extend to engage the firstguide rail means, the slot means being widened above the position of thefirst wheel means when the undercarriage is pulled all the way forwardwith respect to the platform in which position the undercarriage can belifted from the first guide rail means, and the slot means beingnarrowed along the remainder of its length to partially overlie thefirst wheel means to retain them engaged with the first guide railmeans.